The present invention relates to disk drives and storage devices. In particular, the present invention relates to utilizing back electromotive force (BEMF) energy from the spinning spindle motor to retract the head to a safe landing zone during emergency loss of power.
Generally, a magnetic hard disk drive (HDD) includes a magnetic read/write head and several magnetic disks, each disk having concentric data tracks for storing data. The disks are mounted on a spindle motor, which causes the disks to spin. The read/write head is typically mounted on a slider, which is carried by a suspension or load beam. The load beam is attached to an actuator arm of an actuator, which moves the read/write head over the spinning disk during operation. As the disks spin, the slider suspended from the actuator arm flies a small distance above the disk surface. The slider carries a transducing head for reading from or writing to a data track on the disk.
In addition to the actuator arm, the slider suspension comprises a bearing about which the actuator arm pivots. A large scale actuator motor, such as a voice coil motor (VCM), is used to move the actuator arm (and the slider) over the surface of the disk. When actuated by the VCM, the actuator arm can be moved from an inner diameter to an outer diameter of the disk along an arc until the slider is positioned above a desired data track on the disk.
A control circuit is coupled to a coil in the VCM in order to controllably supply current to the coil. When a current is passed through the coil, a motive force is exerted on the actuator arm.
Parking zones in an HDD allow the read/write head to be safely landed after the hard drive has ceased operation. When an HDD is powered down, it usually performs certain operations before actually disconnecting from the external power source. One of these power down operations is to operate the actuator arm to move the head to the parking zone. If the head is not moved to the parking zone prior to power down, the head will land on the disk after the disk stops spinning, potentially damaging the disk and the read/write head.
During emergency loss of power, the read/write head must still be moved to the landing zone to avoid damage to the disk and the read/write head. This situation is referred to as an emergency retract. The problem is where does the power come from necessary to move the read/write head to the landing zone. One solution is to store the necessary energy within the circuit, usually through use of a large capacitor, sufficient to power the VCM during emergency retract. Another solution is to use energy inherent to the operation of the disk drive system to supply power to the VCM and move read/write head to the safe landing zone. The smaller the disk however, the less inherent energy is present to help move the read/write head to the safe landing zone.
Thus, there is a need for a design that can efficiently harness and use the inherent power available in the disk drive system to safely move the read/write head to the parking zone during emergency loss of power.